(1) Field of the Invention
The present invention relates to the processing of output of an effective pixel region and an optical black area of a solid-state image sensor used in a camera.
(2) Description of the Related Art
As shown in FIG. 5, in a conventional photovoltaic surface of a CCD, which is a solid-state image sensor applicable to, for example, a digital camera, there are provided an effective area 50a serving as an effective pixel region in which image signals of pixels (cells) can be read, and an optical black area (OB) 50b in which reference black level signals for correction of the image output signals with regard to the above-mentioned pixels can be read.
Further, output signals from each pixel array of the CCD are sampled-and-held by a correlated double sample-and-hold circuit, subjected to an A/D conversion, temporarily stored in a DRAM, subjected to a compressing process by a compressing/decompressing circuit, and then, stored as image signals in a recording medium such as a memory card.
The compressing process is carried out in such a manner that all the pixel arrays which include the effective area. 50a and the OB area 50b are divided into a predetermined unit block of n (number of pixels) by m (number of pixels), such that output of each pixel is read by the unit block, and subjected to a DCT, and then, Huffman coding processing is conducted. At regeneration, the compressed data in each block is inversely transformed by a decompressing process and image signals are obtained. Incidentally, the compressing process is irreversible, so that the image signals processed by the irreversible compressing process are not exactly the same as the image signals before the compressing process, even if the compressed image signals are decompressed.
With regard to the conventional imaging apparatus described above, the compressing process is conducted in such a manner that the pixel arrays of the CCD are divided into blocks of n by m as described above. However, when all the pixels of the CCD are divided into the blocks, a boundary line L0 between the effective area 50a and the OB area 50b may run through the divided blocks described above like a boundary block 50c, as shown in FIG. 6, owing to the relationship between the number of all the pixels and the number of pixels in divided blocks. When the image signals of the boundary blocks 50c are compressed and regenerated by the decompressing process, the regenerated image of the boundary blocks 50c is not exactly the same as the original image owing to the irreversibility of the compressing process. Therefore, the optical black area affects the effective area, so that the boundary line L0 becomes irregularly fuzzy causing poor quality of the image output.
As shown in FIG. 6, showing an enlarged arrangement of the photovoltaic surface, when all the pixels of the CCD are divided into the blocks 50c, the boundary line L0 may be coincident with a dividing line L1 of the divided blocks. Pixel output signals around the dividing line L1, which lies in the transition area to the optical black area may include noise. When the output signals of the effective area have the noise described above, an imaging signal level in the edge portion of the area may fluctuate, so that the regenerated image has poor quality.
Additionally, in the conventional compressing process, only the effective area is recorded and a black level is determined by a clamping process at the time of recording, so that a stable accuracy of the black level is hardly obtained. Further, it is capable of correcting the black level at the time of recording, but there is a problem that the period of the recording process becomes long.
The present invention is intended to address the problems described above. An object of the present invention is to provide a camera that uses a solid-state image sensor in which fluctuations at a boundary region between an effective pixel region and an optical black area are removed so as to obtain picture signals with high quality; and further, in which a highly accurate black level can be detected and correction is conducted at regeneration.
A first camera in accordance with the present invention includes: a solid-state image sensor having an optical black area at a predetermined region other than an effective pixel region; a correlated double sample-and-hold circuit provided with the solid-state image sensor for sampling-and-holding pixel output of the solid-state image sensor; and a compressing unit for irreversibly compressing output signals of the correlated double sample-and-hold circuit corresponding to the effective pixel region and the optical black area of the solid-state image sensor, respectively; and wherein the solid-state image sensor has a margin area which is provided at a boundary area between the effective pixel region and the optical black area, and the margin area does not contribute to regeneration of an image.
A second camera in accordance with the present invention includes: a solid-state image sensor having an optical black area at a predetermined region other than an effective pixel region; a correlated double sample-and-hold circuit provided with the solid-state image sensor for sampling-and-holding pixel outputs of the solid-state image sensor; and a compressing unit for irreversibly compressing output signals of the correlated double sample-and-hold circuit corresponding to the effective pixel region and the optical black area of the solid-state image sensor, respectively; and wherein the solid-state image sensor has a margin area which is provided at a boundary area between the effective pixel region and the optical black area, and the margin area does not contribute to regeneration of an image, and the width in the line direction of the optical black area is set to 2 times or more by integer the width of the block area as a processing unit in the irreversible compressing process by the compressing unit.
A third camera in accordance with the present invention includes: a solid-state image sensor having an optical black area at a predetermined region other than an effective pixel region; a correlated double sample-and-hold circuit provided with the solid-state image sensor for sampling-and-holding pixel outputs of the solid-state image sensor; and a compressing unit for irreversibly compressing output signals of the correlated double sample-and-hold circuit corresponding to the effective pixel region and the optical black area of the solid-state image sensor, respectively.